FIGS. 1-2 depict plan and side views, respectively, of a portion of a conventional heat assisted magnetic recording (HAMR) transducer 10. The HAMR transducer 10 includes a pole (not shown), coil(s) (not shown), and other components used in writing to a media (not shown). The HAMR transducer 10 is coupled to a laser (not shown) for providing light energy to the HAMR transducer 10. In addition, the HAMR transducer includes a conventional interferometric tapered waveguide (ITWG) 60 for directing light from the laser to a near field transducer (NFT) near the ABS. The conventional ITWG 20 includes a bottom cladding layer 12, a core layer 14, and a top cladding layer 16. The core layer 14 is formed into arms 22 and 24 as well as tapered portion 26. In operation, light is coupled into the ITWG 20 and confined to a smaller mode in tapered region 26. The light is split into the arms 22 and 24. This is typically accomplished using a Y-splitter, as shown in FIG. 1, or a multimode interferometric (MMI) device.
At the ABS, light from the arms 22 and 24 of the ITWG 20 is out of phase. Each arm 22 and 24 is designed to have a different optical length. The differing optical lengths are due to differences in length, thickness and width of the arms 22 and 24. The arms 22 and 24 of the conventional ITWG 20 thus have an optical path difference. When the light from the arms 22 and 24 converges near the ABS, the light from the arm 22 is out of phase from the light from the arm 24 because of this optical path difference. Thus, the arms 22 and 24 have a phase difference. The target phase difference is the desired phase difference between light from the arms 22 and 24 at or near the ABS, for example at the NFT (not shown).
In operation, the conventional ITWG 20 directs light energy from the laser to the NFT (not shown). Light from the arms 22 and 24 having the target phase difference provides a desired interference pattern at the NFT. For example, for some HAMR transducers 10, the target phase difference is 180°. The NFT converts the electromagnetic energy in the interference pattern into surface plasmons at the NFT. The NFT then transfer this energy to a highly localized field, and thus a small spot, at the media. The conventional HAMR head 10 may then use the heat at and/or around the spot to magnetically write to the media.
FIG. 3 depicts a conventional method 50 for forming the conventional ITWG 20. The bottom cladding layer 12, core layer 14 and top cladding layer 16 are deposited, via step 52. The ITWG pattern is then transferred to the waveguide layers 12, 14 and 16, via step 54. Typically, a mask that covers the arms 22 and 24, the tapered portion 26 and any remaining portions of the ITWG 20 is provided. The exposed portions of the top cladding layer 16 and core layer 14 are removed. A portion of the bottom cladding layer 12 might also be removed, for example by over etching the core layer 14. A trench is thus formed in the top cladding layer 16 and core layer 14. The ITWG 20 is thus defined. The areas surrounding the ITWG are refilled with a dielectric 18, via step 56. The top cladding 16, dielectric 18 and bottom cladding 12 layers may be formed of the same material. Thus, the boundaries between the layers 12, 16 and 18 are denoted by dashed lines and the dielectric 18 may be considered part of the top cladding layer 16. The ITWG 20 may thus be formed.
Although the conventional ITWG 20 and method 10 function, there are drawbacks. In particular, efficiency of the NFT may not be sufficient for operation of the conventional HAMR transducer 10. The ability of the NFT to adequately perform its functions depends upon a number of factors. The NFT parameters, such as the NFT shape, size and materials, influence NFT performance. Illumination parameters related to the energy input from the laser and directed by the ITWG 20 also affect NFT performance. The phase difference of the light arriving at the NFT from the arms 22 and 24 is one such parameter. Processing limitations may result in variations in the thickness, width, length, and/or to certain extent the refractive index of the conventional ITWG 20. Variations in the NFT-to-waveguide overlay and voids in the conventional ITWG 20 may also affect the optical path length and thus phase difference between the arms 22 and 24. Further, the laser diode wavelength and temperature variations of the conventional transducer 10 may also affect the phase difference between the arms 22 and 24. The ability of the conventional ITWG 20 to provide light having the target phase difference at the NFT may be adversely affected. If the light from the arms 22 and 24 does not have the target phase difference, the desired interference pattern may be shifted off of the NFT. Performance of the NFT and, therefore, the conventional HAMR transducer 10 may thus be hindered.
Accordingly, what is needed is an improved method for fabricating an ITWG in a HAMR transducer.